Woody Fibre of the Stems of Palms. 61 
habit of seeing old palms cut down knows this to be the fact. 
When the axe is laid to the bottom of some of these old stems, 
it rebounds from them as if it were striking a piece of iron, 
while the upper part can be cut through with the greatest 
facility. Every Brazilian is aware of this fact. So durable 
is the wood of the large species of palm which they call Pati, 
that they prefer it to most other wood for supports to their 
houses, which in the country are generally built of wood, but 
it is only the lower, never the upper portion of the stem that 
they choose. The explanation given above will also account 
for this fact. In the third place, he says, “'The hardness of 
the exterior of palm-stems cannot be owing to the pressure of 
new matter from within outwards, but to some cause ana- 
logous to the formation of heart-wood in exogens. Is there 
any proof that such a cause is in operation?” Before reply- 
ing to this, I may observe, that the opinions of vegetable phy- 
siologists are still unsettled regarding the formation of wood 
in exogenous stems; Lindley, and others, maintaining the 
opinion of Du Petit Thouars, that the wood of a plant is 
formed by the multitude of leaf-buds by which it is covered, 
each of which may be considered a fixed embryo, having an 
independent life and action—that by its elongation upwards 
it forms new branches, and by its elongation downwards it 
forms wood and bark ;—whilst DeCandolle, and most of the 
French physiologists, explain its formation by the hypothesis, 
that new layers are developed by pre-existing layers, which 
are nourished by the descending juices formed in the leaves. 
In palms, a longitudinal section of their stems, with the leaves 
still attached to them, only requires to be seen to convince 
the most sceptical that the heneous substance of them is 
formed by the leaves, and this affords another proof, at least 
an analogical one, to the many which have already been given, 
that the wood of exogens originates in the leaves. The only 
difference between the formation of these two kinds of stems 
seems to be, that in the exogenous tribes the woody fibre al- 
ways remains between the bark and the last-formed layer of 
wood ; while in the stems of palms the bundles of woody tis- 
sue pass downwards and inwards to the interior of the stem, 
then gradually downwards and outwards, and finally descend 
parallel with the axis of the stem, through the previously 
formed tissue of the same nature. 
Organ Mountains, Brazil, May 28, 1837. 
